A popular spring break souvenir may have more staying power than you'd like if it contains the chemical p-phenylenediamine, or PPD.

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Originally published on March 25, 2013 6:59 pm

A henna tattoo looks like a fun beach souvenir — until you break out in a rash and blisters.

The dyes used for the popular temporary tattoos aren't always natural or safe, the Food and Drug Administration warned today. "Black henna" used to make the intricate designs darker often doesn't come from a plant, but from a harsh chemical that causes allergic reactions.

The bad actor is p-phenylenediamine (PPD), a chemical derived from coal tar that can cause skin allergies. It's sold as hair dye, and sometimes people doing henna tattoos use it because it dries faster and has a darker hue than the brownish red of traditional henna.

But PPD isn't supposed to be used on the skin. And the FDA says it has received reports that it is, including a 5-year-old girl with blisters on her forearm two weeks after getting a "henna" tattoo, and a teenager whose back was blistered and raw.

These problems have been cropping up for a while, and aren't restricted to spring break silliness. Henna kiosks are popping up in shopping malls, and are becoming a staple of beach boardwalks and some immigrant enclaves coast to coast.

In 2008, the New England Journal of Medicinereported on a Kuwaiti woman who came to a London hospital after having henna applied to her hands for a wedding. The intricate designs, called mehndi, are traditional for weddings and other celebrations in the Middle East and South Asia. This woman, alas, ended up with big blisters that exactly followed the graceful floral design.

The problems may be due to our modern taste for haste.

A group of Israeli dermatologists note that natural henna, which is made from leaves of the Lawsonia bush, has been used for thousands of years with few problems. But it also takes 2 to 12 hours to impart its distinctive stain, during which time the hennaed person has to endure a thick layer of paste on the adorned body part.

"Our forefathers appeared to be in less of a hurry to see results," the doctors wrote, "and apparently black staining was not the fashion of the time."

This meant they also never reported rash or blisters from the decoration. So take heed of the Israeli doctors message: "It would serve today's customer well if the appliers of henna would stick to the original formula and respect the lessons of the past."